Coplanar waveguide switch

ABSTRACT

A device having a capacitor for changing the impedance of a section of a coplanar waveguide is provided, the capacitance of the capacitor being changeable, the signal line of the section of the waveguide being interrupted for a predefined length, a first connection connecting the ground lines of the waveguide, and the second connection connecting both parts of the interrupted signal line.

BACKGROUND INFORMATION

Micromechanically manufactured high-frequency short-circuiting switchesare made up of a thin metal bridge stretched between the ground lines ofa coplanar waveguide. This bridge is electrostatically drawn to a thindielectric disposed on the signal line, thereby increasing thecapacitance of the plate-type capacitor formed by the bridge and thesignal line. This capacitance between the signal line and the groundline influences the propagation properties of the electromagnetic wavesguided on the waveguide. In the off state (the metal bridge is below), alarge part of the power is reflected. In the on state (the metal bridgeis above), a large part of the power is transmitted.

SUMMARY OF THE INVENTION

The device of the present invention has the advantage that the length ofthe metal bridge, i.e., the length of the second electrically conductiveconnection, is not dependent on the spacing of the ground lines of thecoplanar waveguide, i.e., the spacing of the ground lines of thewaveguide may be selected independently of the length of the secondconnection and vice versa. This results in the advantage that ahigh-frequency microswitch having the features, “minimal spacing of theground lines,” “high operating frequency,” “large expansion of thesecond line, i.e., of the metal bridge,” and “low switching voltage” iseasily produced in accordance with the present invention. Furthermore,it is possible that the inductor serially-connected to the capacitor bythe first electrically conductive connection between the ground lines ofthe coplanar waveguide is selected independently of the design of thesignal line. As a result, it is possible using simple means to achieve alow obstruction of the propagation of the electromagnetic waves alongthe waveguide as well as optimal dimensioning of the first connectiondesigned as a short-circuiting link between the ground lines and thewaveguide.

It is also advantageous that the first and the second connections aremetallic connections. As a result, all of the material-specific andprocess technology-related advantages of using metals as electricallyconductive connections find a use in accordance with the presentinvention.

It is also advantageous that the second connection is mechanicallydeformable such that the spacing of the first connection and the secondconnection is variable in at least one partial area of the secondconnection. As a result, a capacitor having a variable capacitance isproduced using simple means.

It is also advantageous that the capacitance of the capacitor is able tobe changed by an electrostatic force between the first connection andthe second connection. Therefore, simple means are able to be used toprovide two circuit states of the device of the present invention, sothat a reliable and quick switchability of the device is ensured.Moreover, as a result, the circuit state of the device is always clearlydefined.

A further advantage is that the capacitor has a first predefinedcapacitance and a second predefined capacitance as a function of apredefined electrical voltage between the first connection and thesecond connection. As a result, it is possible to determine theoperating frequency largely independently of the distance of the groundlines of the coplanar waveguide by dimensioning the first and secondelectrically conductive connections, in particular, and the dielectriclayer between these two. The insertion attenuation (loss) is alsoadjustable as a result of this.

It is a further advantage that the first connection forms and inductorin series with the capacitor between the signal line and the groundlines. This makes it possible to provide different forms and dimensionsfor the first connection, so that the inductance resulting from thefirst connection is largely predefinable.

Furthermore, it is advantageous that the common impedance of the firstcapacitor and the inductor at an operating frequency essentiallycorresponds to their ohmic resistance. As a result, it is possible toachieve particularly significant insulation, i.e., a particularly largereflection coefficient, when the short-circuiting switch is switchedoff.

Another advantage is that approximately 77 GHz or approximately 24 GHzare provided as the operating frequency. This makes it possible to usethe device of the present invention for ACC (adaptive cruise control) orSRR (short range radar) applications.

In addition, it is advantageous that the predefined length is providedsuch that reflections at a junction between the signal line and thesecond connection compensate for each other. As a result, the insertionattenuation of the switch and, thus, the adaptation in the on state areimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of a device of the present invention having acapacitor.

FIG. 2 shows a sectional view along line of intersection C from FIG. 1of the device of the present invention having a capacitor.

FIG. 3 shows a sectional view along intersection line A from FIG. 1 ofthe device of the present invention having a capacitor.

FIG. 4 shows a sectional view along line of intersection B from FIG. 1of the device of the present invention having a capacitor.

FIG. 5 shows a perspective view of the device of the present inventionhaving a capacitor.

FIG. 6 shows an equivalent circuit diagram of the device of the presentinvention having a capacitor.

DETAILED DESCRIPTION

FIG. 1 shows a micromechanical high-frequency short-circuiting switch asan example of the device of the present invention having a capacitor. Inthe case of the device of the present invention, a coplanar waveguide isdisposed on a substrate 100. In accordance with the present invention,the coplanar waveguide includes three coplanar, electrically conductivelines, in particular, which are essentially parallel to one another atleast locally. The lines of the coplanar waveguide are designed to bemetallic in particular and are disposed on the substrate particularly byone or more galvanic process steps. In accordance with the presentinvention, substrate 100 has, in particular, the characteristic of asmall loss angle. The two outer lines of the three lines of the coplanarwaveguide correspond to a first ground line 110 and a second ground line111, and the middle line corresponds to a signal line 120 of thecoplanar waveguide. FIG. 1 shows a top view of a detail relevant for thedevice of the present invention of such a coplanar waveguide disposed onsubstrate 100. Both ground lines 110, 111 of the coplanar waveguide areconnected via a first electrically conductive connection 130. In thiscontext, first connection 130 is disposed directly on substrate 100 andis a low in “height” in comparison with the “height” of ground lines110, 111, i.e., first connection 130 connects to the “foot” of groundlines 110, 111 on substrate 100. Signal line 120 of the coplanarwaveguide is interrupted in the region of first connection 130.Therefore, connection 130 is also not connected in an electricallyconductive manner to signal line 120. In accordance with the presentinvention, a layer of a dielectric not shown in FIG. 1 is deposited onfirst connection 130 in the region of the interruption of signal line120. Furthermore, interrupted signal line 120 is connected via a secondelectrically conductive connection 121. In this context, in accordancewith the present invention, second connection 121 is provided inparticular in the form of a metal bridge between the ends of interruptedsignal line 120. However, in accordance with the present invention,second connection 121 is provided at a certain distance to the plane ofsubstrate 100, the distance of second connection 121 to substrate 100 orto first connection 130 corresponding approximately to the height ofsignal line 120. As a result, in the absence of forces on secondconnection 121, second connection 121 “floats” between the ends ofinterrupted signal line 120. In this respect, second connection 121 isalso referred to as bridge or metal bridge 121. FIG. 1 also shows afirst line of intersection designated by the letter C, a second line ofintersection designated by the letter A, and a third line ofintersection designated by the letter B. The first line of intersectioncuts the device of the present invention vertically with respect to thecourse of ground lines 110, 111 and of signal line 120 in the region offirst connection 130 between ground lines 110, 111. The second line ofintersection cuts the device of the present invention parallel to thecourse of lines 110, 111, 120 of the coplanar waveguide in the region offirst ground line 110. The third line of intersection cuts the device ofthe present invention parallel to the course of lines 110, 111, 120 ofthe coplanar waveguide in the region of signal line 120 or where signalline 120 is interrupted, in the region of second connection 121.

FIG. 2 shows a sectional view of the device of the present inventionalong the first line of intersection (letter C) from FIG. 1. Substrate100, first ground line 110, and second ground line 111 of the coplanarwaveguide are shown in turn. Signal line 120 of the waveguide issituated between ground lines 110, 111 of the coplanar waveguide. Thespatial arrangement of first connection 130 and of second connection 121with respect to their distance from the surface of substrate 100 becomesparticularly clear in FIG. 2. In FIG. 2, first connection 130 isdisposed directly on substrate 100, while second connection 121 isdisposed on signal line 120 and is, thus, provided at a distanceequaling the height of signal line or ground lines 110, 111, 120 fromthe plane of substrate 100.

FIG. 3 shows a sectional view of the device of the present inventionalong line of intersection A from FIG. 1. Only substrate 100 and firstground line 110 are visible.

FIG. 4 shows the device of the present invention along the third line ofintersection (letter B). Signal line 120 of the coplanar waveguide isprovided on substrate 100. Signal line 120 is interrupted for apredefined length 122. In this region, second connection 121 bridgessignal line 120. In this context, second connection 121 connects the twoends of signal line 120 created by the interruption of signal line 120.In the exemplary embodiment, second connection 121 is providedparticularly at a distance from substrate 100 corresponding to theheight of signal line 120. FIG. 4 also shows first connection 130.Dielectric layer 140, which was already mentioned in connection withFIG. 1, is situated above first connection 130.

FIG. 5 shows a perspective view of the device according to the presentinvention. First ground line 110 and second ground line 111 of thewaveguide are situated on substrate 100. Interrupted signal line 120 issituated between these ground lines 110, 111. Both ends of signal line120 are bridged by second connection 121. FIG. 5 also shows dielectriclayer 140. First connection 130 between ground lines 110, 111 providedbelow dielectric layer 140, i.e., in the direction of substrate 100, isnot represented because of the perspective view in FIG. 5.

FIG. 6 shows an equivalent circuit diagram of the configurationaccording to the present invention. In the equivalent circuit diagram,both ground lines 110, 111 are only represented in the form of a singleline of the coplanar waveguide. This is because ground lines 110, 111are at the same potential. Signal line 120 of the coplanar waveguide isalso shown in FIG. 6. A capacitor 200 and an inductor 210 are arrangedin series between signal line 120 and ground lines 110, 111. Capacitor200 is at least partially produced by first connection 130 and secondconnection 121, which are both not shown in FIG. 6. In accordance withthe present invention, capacitor 200 is designed to have a variablecapacitance, namely particularly as a result of second connection 121being mechanically deformed and its distance to first connection 130being consequently changed at least in partial areas, therebyinfluencing the capacitance of capacitor 200. Inductor 210 isessentially produced by first connection 130. Patterning firstconnection 130, which acts as a direct-voltage short circuit betweenground lines 110, 111, produces an inductance that is specifiable bychanging the length-width ratio, the form, e.g. meander-shaped or thelike.

FIGS. 4 and 5 show mechanically deformable second connection 121 for thecase that the represented sections of the coplanar waveguide have a hightransmission coefficient and a low reflection coefficient. The spacingof first connection 130 and second connection 121, which together withthe electrical properties of dielectric layer 140 largely determines thecapacitance of capacitor 200, are shown with maximum distance in FIG. 4.The capacitance of capacitor 200 is very small in this case and isdecisive for the input attenuation of a short-circuiting switch, forexample. For the case that an electrical voltage, e.g. a direct voltage,is applied between first connection 130 and second connection 121, anelectrostatic attractive force results between first connection 130 andsecond connection 121. Consequently, since second connection 121 ismechanically deformable, it is deformed and drawn at least in a partialarea, namely essentially in the middle of the metal bridge, to firstconnection 130 or to dielectric layer 140 deposited on first connection130. The dielectric, in particular silicon dioxide or silicon nitride,prevents the device configured in particular as a switch from beinggalvanically contacted in the off state. As a result, the capacitance ofcapacitor 200, which is substantially formed by first connection 130 andsecond connection 121, changes so that it becomes greater. In accordancewith the present invention, applying or removing an electrical voltagebetween both connections 130, 121 changes the capacitance of capacitor200 of the device of the present invention or switches it in the case ofthe device being configured as a switch. The position of secondconnection 121 represented in FIGS. 4 and 5 corresponds to the tandem(switched-through) operation of the device and is switched as an onstate. The state not shown in FIG. 4 in which a second connection 121 isattracted by an electrical voltage to first connection 130 correspondsto a switched-off switch. This is the case because it is provided inaccordance with the present invention that the waveguide, which includessections represented in FIGS. 1 through 4, is operated at a predefinedoperating frequency. The capacitance of capacitor 200 assumes as afunction of an electrical voltage between both connections 130, 121 twocapacitance values, which are designated in the following as firstcapacitance value or also first capacitance and second capacitance valueor also second capacitance. The first capacitance corresponds to the offstate, i.e., second connection 121 is drawn to first connection 130 as afunction of the applied electrical voltage. Accordingly, the secondcapacitance corresponds to the on state shown in FIG. 4 where secondconnection 121 is not mechanically deformed. In accordance with thepresent invention, the first capacitance and the second capacitance aredetermined by a variation in particular in the width and length of firstconnection 130 and of second connection 121 as well as in the thicknessand the material properties of the dielectric layer and in the height ofsignal line 120. In accordance with the present invention, it isprovided in particular that connections 130, 121, dielectric layer 140,and signal line 120 are dimensioned such that the impedance of a seriesconnection of the first capacitor and an inductor formed by firstconnection 130 is eliminated at the operating frequency or is kept asminimal as possible. According to the present invention, inductor 210 isessentially adjusted by the dimensioning and form design of firstconnection 130 between ground lines 110, 111 of the waveguide.

In accordance with the present invention, second connection 121 is athin metal bridge stretched between the ends of interrupted signal line120 of the waveguide. First connection 130 acts as a direct-voltageshort circuit between ground lines 110, 111. First connection 130 actstogether with second connection 121 as a plate-type capacitor. As aresult of suitable dimensioning and form design of the direct-voltageshort circuit, i.e., of first connection 130, an inductor in series withthe plate-type capacitor is able to be adjusted (at operatingfrequency). The inductor being in series with the plate-type capacitorforms a series resonant circuit whose resonant frequency in the offstate of second connection 121 is at the operating frequency of thedevice as a result of suitably dimensioning the inductance and thecapacitance of the plate-type capacitor. As a result, the impedancebetween signal line 120 and ground lines 110, 111 is significantlyreduced with respect to the impedance of the pure plate-type capacitor(without inductance), thereby significantly improving the insulation ofa device configured as a high-frequency switch. At this point, theinsulation is limited by the ohmic losses in second connection 121 andin first connection 130. In an on state, as a result of the reducedcapacitance of the plate-type capacitor (second connection 121 or alsobridge 121 “above,” i.e., at a relatively great distance from thesubstrate), the device or the component or structural element isoperated at operating frequency outside of this resonant frequency, sothat no greater insertion attenuations result. If the length of secondconnection 121 is suitably dimensioned (e.g. half of the effectivewavelength at the operating frequency), the reflections compensate foreach other at the points of contact or the junction points between thecoplanar waveguide (i.e., the ends of signal line 120) and secondconnection 121, thereby improving the insertion attenuation of thedevice provided, for example, as a switch and, consequently, theadaptation. This corresponds to a transformation of the impedance ofsecond connection 121 to the impedance of the coplanar waveguide. Thelength of second connection 121 is not limited by a maximum spacing ofthe ground lines at high operating frequencies. As a result, anincreased switching voltage, i.e. the voltage to be applied betweenfirst and second connection 130, 121, does not need to be used at higheroperating frequencies.

In accordance with the present invention, provision is made inparticular for selecting the operating frequency in the range ofapproximately 77 GHz or approximately 24 GHz. As a result, the device ofthe present invention is suitable for applications in the area of ACC(adaptive cruise control) or SRR (short range radar).

What is claimed is:
 1. A device comprising: a capacitor for changing animpedance of a section of a coplanar waveguide, the capacitor having achangeable capacitance, the section of the waveguide having a signalline which is interrupted for a predefined length, the waveguide havingground lines; and first and second electrically conductive connectionsat least partially surrounded by the capacitor, the first connectionconnecting the ground lines of the waveguide, the second connectionconnecting two parts of the interrupted signal line.
 2. The deviceaccording to claim 1, wherein the first connection forms an inductor inseries with the capacitor between the signal line and the ground lines.3. The device according to claim 2, wherein a common impedance of thecapacitor and of the inductor at an operating frequency substantiallycorresponds to their ohmic resistance.
 4. The device according to claim3, wherein the operating frequency is about 77 GHz.
 5. The deviceaccording to claim 3, wherein the operating frequency is about 24 Ghz.6. The device according to claim 1, wherein the first and secondconnections are metallic connections.
 7. The device according to claim1, wherein the second connection is mechanically deformable such that aspacing of the first connection and the second connection is changeableat least in a partial area of the second connection.
 8. The deviceaccording to claim 1, wherein a change in the capacitance of thecapacitor is able to be produced by an electrostatic force between thefirst and second connections.
 9. The device according to claim 1,wherein the capacitor has a first predefined capacitance and a secondpredefined capacitance as a function of a predefined electrical voltagebetween the first connection and the second connection.
 10. The deviceaccording to claim 1, wherein the predefined length is such thatreflections at a junction between the signal line and the secondconnection compensate for each other.